fix(dashboard): restore navigation by correcting Top Up sheet markup and click handling

Replace invalid nested anchors with a single anchor per method (Bank, Mobile Money).
Convert placeholder items (Agent, Card) to buttons; bind demo alert only to placeholders.
Add capture-phase guard so real links aren’t intercepted by stale handlers.
Style placeholder buttons to match cards.
Files:

c:\xampp\htdocs\Flowpesa\dashboard.php
c:\xampp\htdocs\Flowpesa\js\dashboard.js
c:\xampp\htdocs\Flowpesa\css\style.css
Test plan:

Hard refresh, open Top Up, click Bank/Mobile → navigates.
Agent/Card show demo alert only.
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